Andrea Mancuso was working just north of the World Trade Center on September 11, 2001, when two planes struck the towers. Soon after, she was the only person around who seemed to have cell phone service.

"I walked from downtown to Lincoln Center (about 4.5 miles) before I was able to hail a cab with four strangers," she said. "Everyone was upset, and no one had a cell phone signal except me. I passed my phone around like a hot potato all the way to Harlem. Everyone including the cab driver graciously and tearfully called their families."

Her story, of course, is not unique. For hours, family members and co-workers frantically tried to contact people they knew in Lower Manhattan.

The network failure could partially be pinned on infrastructure damage. Cell towers were destroyed in the attacks, along with switching equipment used for landline phones. But another cause of the problem was the huge surge in traffic from people trying to find loved ones or letting others know they were OK.

Undoubtedly, with each crisis, operators have learned more about what they can do to keep service up and running. But there's a flip side to that growing expertise: we're more dependent than ever on cell phones.

In September 2001, there were between 118 million and 128 million wireless subscribers who owned cell phones, according to data compiled by the CTIA Wireless Association. At the end of 2010, it was 302 million, or more than 96 percent of Americans. To keep up with the surge, wireless operators have spent billions of dollars upgrading their networks, adding more than 125,000 new cell sites since the end of 2001.

But is that enough? Despite anecdotal evidence to the contrary, industry experts interviewed by CNET believe that carriers have made huge strides on network reliability by doing simple things like expansion and adding generator backups, and complex things like forming emergency response units. They believe we're in far better shape than we were 10 years ago...to a point.

"There's no question the networks are in a much better position today than they were in 2001 to handle a significant crisis, even in the face of a staggering increase in users," said Charles Golvin, an analyst at Forrester Research. "But it's also important for people to make contingency plans for communications, in case the network isn't working."

On the plus side
There's reason for that guarded optimism. Carriers have added spectrum and high-capacity connections from their cell towers to the wired networks that transport voice and data traffic. And they've hardened their networks with equipment that can withstand heavy wind and rain, as well as ensure that the equipment remains functional when commercial power is lost.

In fact, all the major wireless carriers have increased the number of cell sites with backup power supplies. They've also increased the number of cell sites on wheels that they can roll into locations that have had infrastructure damage.

"A good proportion of the cellular bay stations across all the major carriers now have some kind of battery or generator for backup power," said Gerard Hallaren, an equities analyst at JRPG Research. "That wasn't the case back in 2001."

Verizon Wireless, for example, has for years been installing backup generators and batteries to many of its cell sites. During the 2003 blackout that kept much of the Northeast in the dark for hours, Verizon's customers could still communicate when customers from other carriers could not.

There's also that human element, in terms of specialized units that can quickly move into an area.

"In the event of a natural or man-made disaster, like 9/11, we have multiple groups within AT&T who are equipped to respond quickly to repair and restore network capabilities," AT&T spokesman Mark Siegel said. "Our network disaster recovery team is a great example of that. They were deployed after 9/11 to assist in restorations, and we've invested $600 million in our NDR team since its formation."

There are also new services. Enhanced 911, which allows 911 operators to locate callers on a cell phone, is a prime example. A decade ago, cell phones in the U.S. didn't yet support the technology. Today, every phone sold in the U.S. is capable of providing location information to emergency 911 operators.

While it was gaining popularity in Europe and elsewhere in 2001, SMS text-messaging services in the U.S. weren't used much by wireless subscribers because they worked only within carrier networks. This meant that on September 11, 2001, if someone wanted to send a text message to a family member or loved one, they were able to send it only to someone who subscribed to the same carrier.

A few months later, in November 2001, carriers began to connect their networks for text messaging, allowing subscribers on different networks to exchange texts. Today, more than 187 billion text messages cross U.S. wireless networks each month.

Text messaging has become a critical form of communication during a crisis. In the lead-up to Hurricane Irene on the East Coast last month, wireless operators and public-safety officials were asking consumers to use text messaging during the storm instead of making voice calls to help alleviate network congestion.

Text messaging is a better way of communicating in a crisis for several reasons. To start, the messages are small and consume only a small amount of network resources. Second, messages are sent on a cell phone's signaling channel. This means that they're in a separate "lane" from voice and data messages, so they may have a clear path when the voice network is congested. And if the network is too congested even to send a text, the message can be stored. When service resumes, the message is sent.

The technology has become such a ubiquitous and reliable form of communication during an emergency that the Federal Communication Commission is working on rules to allow 911 call centers to accept SMS text messages, as well as photos, videos, and data communications, to provide more information to first responders for assessing and responding to emergencies.

Congestion problem
The biggest problem wireless networks face today in a crisis is a rapid increase in usage. The networks don't have enough capacity to handle the surge in call volume. Cellular networks are designed to handle a certain amount of calls in each cell site or region, with wireless operators carefully calculating how much usage is needed to serve the average usage volume while having just enough capacity to handle spikes in demand.

The problem occurs when a disaster hits, and thousands of people all at once pick up their phones to call someone, send a text message, update Twitter, and so on. There simply isn't enough capacity in the network to allow everyone in a cell site to make a phone call at the same time.

"Crisis situations are a perfect example of why it's so important that the government makes more wireless spectrum available," he said.

While more spectrum could help, it's unclear if it would ever be cost-effective for wireless operators to configure their networks to withstand the highest demand for network resources. Analyst Gerard Hallaren said most networks are designed to handle only about 20 percent to 40 percent of maximum traffic, with 40 percent being on the conservative side.

"It's just economic insanity for any carrier to try to solve the congestion problem," he said. "It's cost-prohibitive to build a network that could serve 330 million at the same time. A service like that would cost hundreds of dollars a month, and people are not willing to pay that much for cell phone service."

That said, the carriers say they've made improvements to their networks and are trying to alleviate the issue.

"We continue to build redundancies into our network and increase capacity so that it is not overwhelmed by 'sudden calling events,'" AT&T's Siegel said.

New generations of cellular technology have also helped make wireless more available during a crisis. The move from 2G to 3G, and now to 4G, will offer carriers more efficiencies in how they use their spectrum, which could also be a benefit during an emergency to alleviate network congestion.

The other major difference between September 2001 and now is that the mobile Internet as we know it today did not exist. Third-generation, or so called 3G, wireless networks were not deployed, and most people did not have access to the Internet from their cell phones. Facebook, Twitter, and other social-networking apps that people access easily from their cell phones today to share pictures, updates, and other information weren't even invented back then. While this traffic also increases the load on networks, sometimes it's easier for users to get through to these sites than to make voice connections via their cell phones.

"People have so many more ways of communicating with each other now to tell someone where they are or that they are all right," Forrester's Golvin said. "Having these communication alternatives is a huge improvement over where we were a decade ago."

Public-safety officials had their own communications challenges responding to the terrorist attacks on September 11, 2001. Tomorrow CNET will explain the problems first responders had that day and why the public-safety community is still waiting for their own wireless network.

About the author

Marguerite Reardon has been a CNET News reporter since 2004, covering cell phone services, broadband, citywide Wi-Fi, the Net neutrality debate, as well as the ongoing consolidation of the phone companies. E-mail Maggie.
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